1. Field of the Invention
The present invention relates to a compression-ignition internal combustion engine having a combustion heater, and specifically to a compression-ignition internal combustion engine having a combustion heater for introducing combustion gas into an intake system of the internal combustion engine.
2. Description of the Related Art
When it is cold, it is necessary to facilitate warm-up of the internal combustion engine.
For this purpose, Japanese Patent Application Laid-open No. 62-75069, for example, discloses a technology for providing a combustion heater, independently of the internal combustion engine body, in an intake system of the internal combustion engine, introducing a combustion gas emitted from the combustion heater into the intake system, and facilitating warm-up of the internal combustion engine by utilizing combustion heat of the combustion gas.
In general, the combustion heater emits the combustion gas including a higher density of carbon dioxide when the combustion heater is used in a normal state, that is, under atmospheric pressure as compared with an exhaust gas of the internal combustion engine, and particularly of the compression-ignition internal combustion engine. Consequently, in the internal combustion engine in which the combustion gas from the combustion heater is introduced into the intake system as shown in the technology described in the above Japanese Patent Application Laid-open No. 62-75069, an intake air having a high density of carbon dioxide is used for engine combustion. In this case, therefore, oxidation reactions of hydrocarbon and carbon monoxide to form carbon dioxide become difficult to proceed. As a result, a larger amount of free hydrocarbon and carbon monoxide exist in the exhaust gas emitted from the internal combustion engine.